Engine retarding devices of the compression release type are commonly utilized in work machines such as on-highway trucks and the like. A compression release brake assembly utilizes compression within the truck's engine to assist the truck's main braking system in order to slow the truck. In effect, such compression release brake assemblies convert the truck's internal combustion engine into an air compressor in order to develop retarding horsepower which is utilized to assist in slowing the truck.
Compression release brake assemblies which have heretofore been designed typically include a hydraulic system having a master cylinder having a piston which is actuated by a cam lobe or push rod associated with an exhaust valve, intake valve, or fuel injector corresponding to a first engine cylinder. Actuation of the piston associated with the master cylinder controls actuation of a piston associated with a slave cylinder which selectively opens and closes an exhaust valve near the end of the compression stroke thereby causing the mechanical work performed during the compression stroke to be dissipated and hence not "recovered" during the subsequent power stroke. It should be appreciated that the exhaust valve opened by the slave cylinder may be associated with either the first engine cylinder, or may alternatively be the exhaust valve associated with a second, different engine cylinder.
However, such heretofore designed compression release brake assemblies have a number of drawbacks associated therewith. For example, such heretofore designed compression release brake assemblies are relatively mechanically complex and often require a relatively large number of repairs during the useful life of the engine. In addition, such mechanical complexity generally increases the costs associated with manufacture of the engine. Yet further, such heretofore designed compression release brake assemblies typically have limited design freedoms in regard to the opening of the respective exhaust valves during braking since actuation of the respective master cylinders must be selected from a cam lobe or push rod associated with an intake valve, exhaust valve, or fuel injector which is the "closest fit" to the timing requirements of the individual exhaust valves.
In an effort to overcome the above-mention drawbacks, a number of compression release brake assemblies have been designed for use in conjunction with a hydraulically-powered fuel injection system. In such devices, the hydraulic supply system which is utilized to operate the fuel injectors of the engine is also utilized to operate the compression release brake assembly. However, such systems typically require modification to the exhaust valves in order to allow an actuator such as a hydraulic piston to contact the stem of the exhaust valve. Such modification to the exhaust valve undesirably increases costs associated with manufacture of the engine.
What is needed therefore is a method and apparatus for operating a compression release brake assembly which overcomes one or more of the abovementioned drawbacks.